Is the Apple pencil compatible with the iPad Mini 4

No, only the iPad Pro

No. The Pencil requires the extra hardware in the iPad Pro's screen to work correctly. It will not even work as a regular capacitive stylus, since its tip is plastic instead of soft rubber.

http://mashable.com/2015/09/09/apple-pencil-ipad-pro-only/#7lOSsvROWgqI

Another no,

Find another smart stylus to use with your iPad model.

I recommend Adonit stylii

http://www.adonit.net/